Generally, in reflector antenna mounted on communication satellite, a diameter thereof is determined so that it has an optimal EOC gain. In particular, a parabolic antenna accommodating two or more frequencies adjusts a diameter of aperture in order to meet EOC directivity at the two frequencies.
In a conventional method for determining a diameter of such reflector antenna mounted on communication satellite, pattern results for each frequency are analyzed by calculating a frequency, a predetermined antenna diameter and antenna structure data as input values.
FIG. 1 is a flowchart for describing a conventional method for determining a diameter of a reflector antenna mounted on communication satellite, wherein a procedure for determining a diameter of a parabolic antenna accommodating two frequencies is illustrated.
First of all, electrical characteristic values such as a frequency, an EOC gain, a sidelobe level, and an X-polarization level are set up at step 101.
Thereafter, a first frequency, an antenna diameter variable value and an antenna geometry variable value are inputted as parameters for the first frequency at step 102, and pattern calculation (simulation) is performed at step 103. Next, an EOC gain acquired by the pattern calculation is analyzed at step 104. In the analysis, if the EOC gain is within the set value range at step S105, the process of the prior art goes to step 106 to carry out a procedure for a second frequency. If the EOC gain is out of the set value range at step 105, the process increases/decreases the antenna diameter variable value depending on a prescribed rule at step 106, and then returns to step 103 to repeatedly perform the processes as described above.
In the meantime, if an antenna diameter for the first frequency is determined, a second frequency, an antenna diameter variable value and an antenna geometry variable value are inputted as parameters for the second frequency at steps 107 and 108, and pattern calculation (simulation) is performed at step 103. And then, an EOC gain acquired by the pattern calculation is analyzed at step 104. In the analysis, if the EOC gain is within the set value range at step 105, the process goes to step 109 wherein an antenna diameter meeting the two frequencies is determined. However, if the EOC gain is out of the set value range at step 105, the process increases/decreases the antenna diameter variable value depending on the prescribed rule at step 106, and then returns to step 103 to repeatedly perform the processes as set forth above.
Upon completion of the processes of the steps 101 to 108, two antenna diameters are determined for the two frequencies, i.e., the first and second frequencies. Then, in order to accommodate the two frequencies in one antenna, the process further performs steps 109 and 110 to determine an optimal one of the two diameters that meets EOC directivity at the two frequencies.
That is, the antenna diameter variable values determined for the first and the second frequencies are compared with each other at step 109. If the two values are not the same, the process increases/decreases the antenna diameter variable values depending on the prescribed rule, and then returns to step 103 to repeatedly perform the above-mentioned processes. If the two values are the same, the process determines the antenna diameter variable values determined for the first and the second frequencies as the optimal antenna diameter at step 110.
In the above-mentioned conventional method for determining the antenna diameter, however, it is required to repeatedly carry out the same calculation procedure with respect to each frequency, and is also difficult to find an optimal antenna diameter if the difference between the two frequencies is large or many frequencies are used.